 
(* ::Section:: *)
(* SIS *)
(* ::Text:: *)
(*SIS[p] can be used as input for 3-dimensional $\sigma ^{\mu }p_{\mu }$ with 4-dimensional Lorentz vector p and is transformed into PauliSigma[Momentum[p]] by FeynCalcInternal..*)


(* ::Subsection:: *)
(* Examples *)
SIS[p]

SIS[p]//FCI//StandardForm

SIS[p,q,r,s]

SIS[p,q,r,s]//StandardForm

SIS[q].(SIS[p]+m).SIS[q]
